Some of a variety of imaging apparatus, such as video camcorders and still cameras, are what is called a collapsible-type imaging apparatus in which a lens barrel that accommodates a variety of optical parts, such as lenses, and optical devices is provided in an extendable/retractable manner and the lens barrel is retracted into an apparatus body when no image is captured while extended from the apparatus body for zoom magnification change and other operation when an image is captured (see Japanese Patent No. 4,504,697, for example).
Providing such a retractable lens barrel allows size reduction when no image is captured (reduction in thickness) and ensures satisfactory optical performance when an image is captured at the same time.
An example of the configuration of a lens barrel in an imaging apparatus of related art will be described below (see FIG. 14).
A lens barrel a includes a fixed ring b, a rectilinear cam ring c unable to rotate around the optical axis but guided by the fixed ring b along the optical axis and moved therealong, a rectilinear guide ring d guided by the rectilinear cam ring c along the optical axis and moved therealong, a second cam ring e, a rectilinear guide/movable frame f guided by the rectilinear guide ring d in the optical axis direction and moved therealong in response to the rotation of the second cam ring e around the optical axis, and a first-group frame g guided by the rectilinear guide ring d in the optical axis direction.
The fixed ring b supports a rotary ring h in such a way that the rotary ring h is rotatable around the optical axis and movable along the optical axis, and the rotary ring h holds the rectilinear cam ring c and supports a first cam ring i in such a way that the first cam ring i is movable along the optical axis. The first cam ring i rotates in response to the rotation of the rotary ring h around the optical axis.
The second cam ring e supports a movable frame j in such a way that the movable frame j is movable along the optical axis.
The first-group frame g holds a first lens group k. The movable frame j holds a second lens group l. The rectilinear guide/movable frame f holds a third lens group m.
The second cam ring e is located on the inner circumferential side of the rectilinear cam ring c, and the rectilinear guide ring d is located on the inner circumferential side of the second cam ring e. When the lens barrel is extended, the first cam ring i, the second cam ring e, and the rectilinear guide ring d protrude toward a subject relative to the rotary ring h and the rectilinear cam ring c, and the first-group frame g further protrudes toward the subject relative to the first cam ring i, the second cam ring e, and the rectilinear guide ring d.
In the thus configured lens barrel, the rectilinear guide ring d is connected to the first-group frame g, which is moved to a point closest to the subject, and the rectilinear guide ring d is guided by the rectilinear cam ring c along the optical axis because a guided protrusion n provided on the rectilinear guide ring d slidably engages with a guide groove o formed in the rectilinear cam ring c and extending along the optical axis.